In general, synthetic quartz glass substrates are manufactured by cutting a synthetic quartz glass block into plates by a cutting tool such as wire saw, lapping the glass plates with an abrasive slurry, and polishing the glass plates until the desired size, thickness and flatness are reached.
When high-precision large-size synthetic quartz glass substrates required to have a high surface flatness are manufactured, the steps of measuring a substrate surface for topological distribution of raised and recessed portions, and partially polishing away the raised portions on the substrate surface on the basis of the measured data are necessary in order to achieve the desired surface accuracy.
As the method for partially controlling a polishing allowance on a substrate surface, Patent Document 1 proposes a method of selecting one tool from a plurality of tools having different working areas, and controlling the rate of moving the tool in accordance with a particular position on a substrate, for thereby controlling a polishing allowance at each position. Also, Patent Document 2 describes a method of moving forward and backward a polishing tool on a substrate, the polishing tool having a smaller polishing surface than the surface of the substrate to be polished, and controlling the pressure applied to the polishing tool through a pressure fluid. Patent Document 3 describes a method of polishing a substrate, comprising the steps of applying a pressure fluid to the substrate from its back surface to partially pressurize the substrate, and forcing abrasive cloth to the substrate via a jig.